It is necessary in some operations to accomplish relative axial movement of a device or a part of a device that is disposed in an earth borehole. One type of apparatus utilized for this purose is a shifting tool that is run into a borehole on a wireline. Such a wireline shifting tool in accordance with the prior art has utilized extendable and retractable upwardly facing upper dogs and downwardly facing lower dogs, with various means for extending and retracting the dogs. One set of dogs engages the part to be shifted and the other engages a member fixed relative to the part to be shifted. Power is then applied to move the dogs further apart and consequently shift the part to be shifted.
A serious difficulty has been experienced in such prior art apparatus due to inability to retract the dogs and retrieve the shifting tool from the borehole in the event of a malfunction. The problem is especially acute when upwardly facing dogs can not be retracted. Problems have also been encountered in prior art apparatus in connection with the proper positioning of the tool relative to the device to be shifted.
It is accordingly the general object of this invention to provide improved wireline shifting tool apparatus and methods that obviate the difficulties and problems above mentioned.
For a further understanding of the invention and further objects, features, and advantages thereof, reference may now be had to the following description, taken in conjunction with the accompanying drawings.